Dynamics of the late-winter ENSO teleconnection to the North Atlantic-European region

• Main Author: Mezzina, Bianca
• Other Authors: García Serrano, Javier, Bladé, Ileana, Universitat de Barcelona. Facultat de Física
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universitat de Barcelona 2021
• Subjects: Climatologia; Corrent del Niño; Geomorfologia climàtica; Canvi climàtic; Interacció oceà-atmosfera; Climatology; El Niño Current; Climatic geomorphology; Climatic change; Ocean-atmosphere interaction; Pacific; North Atlantic; North Atlantic oscillation
• Online Access: http://hdl.handle.net/2445/182562; http://hdl.handle.net/10803/673236

[eng] The El Niño-Southern Oscillation (ENSO) is a natural mode of climate variability in the tropical Pacific, which not only perturbs the local atmosphere, but whose impacts can also reach remote, extra-tropical regions through atmospheric teleconnections. While the atmospheric response to ENSO and the dynamics of its teleconnections are well assessed in certain locations, such as the North Pacific-American sector, it is not the case for the North Atlantic-European (NAE) sector. In this thesis, the dynamics of the ENSO-NAE teleconnection are assessed in late winter (January-March), the season in which a significant and robust ENSO-related signal has been reported in the literature. Part of this well-known late-winter ENSO signal is a sea-level pressure (SLP) dipole in the North Atlantic. In this thesis, it is assessed that this “canonical” dipole is mostly driven by tropospheric dynamics and is related to the large-scale Rossby wave train triggered from the tropical Pacific by the anomalous upper-level divergence associated with ENSO. The “canonical” SLP dipole is known to be reminiscent of the surface signature of the North Atlantic Oscillation (NAO), which is the dominant mode of variability in the North Atlantic. The relationship between the ENSO-forced response in the NAE region and the NAO is examined: it is found that no further similarities are evident apart from the surface SLP signature, and it is suggested that ENSO and the NAO are largely unrelated. Another issue tackled in this thesis is the (a)symmetry of the atmospheric signal associated with the two phases of ENSO, El Niño and La Niña, which show roughly opposite patterns of sea surface temperature (SST) anomalies in the tropical Pacific but not necessarily a symmetric atmospheric response. It is noticed that, in a set of sensitivity experiments with three state-of-the-art models, the extra-tropical response in the troposphere is slightly asymmetric in amplitude and longitudinal location. However, it is highlighted that the mechanisms at play, ...